Variety Of Semiconductor Materials Research Articles

Non-equilibrium longitudinal optical phonons and their lifetimes

Non-equilibrium phonons have been discussed for almost six decades. Here, the nature of the longitudinal optical mode, particularly in polar materials, is discussed along with its lifetime and bottleneck occurrences. The history of non-equilibrium phonons is discussed along with their generation by the relaxation of hot carriers. The role of inter-valley scattering and phonon lifetime is introduced along with the concept of a phonon bottleneck. Various methods of lifetime measurement are introduced. Measurements of the lifetime in a variety of semiconductor materials is reviewed and a possible scaling behavior discussed.

Recent Progress of Transition Metal Phosphides for Photocatalytic Hydrogen Evolution.

Photocatalytic hydrogen evolution can effectively alleviate the troublesome global energy crisis by converting solar energy into the chemical energy of hydrogen. In order to realize efficient hydrogen generation, a variety of semiconductor materials have been extensively investigated, including TiO2 , CdS, g-C3 N4 , metal-organic frameworks (MOFs), and others. In recent years, to achieve higher photocatalytic performance and reach the level of large-scale industrial applications, photocatalysts decorated with transition metal phosphides (TMPs) have shone brightly because of their low cost, stable physical and chemical properties, and substitution for precious metals of TMPs. This Review highlights the preparation methods and properties associated with photocatalysis of TMPs. Moreover, the H2 generation efficiency of photocatalysts loaded with TMPs and the roles of TMPs in catalytic systems are also studied systematically. Apart from being co-catalysts, several TMPs can also serve as host catalysts to boost the activity of photocatalytic composites. Finally, the development prospects and challenges of TMPs are put forward, which is valuable for future researchers to expand the application of TMPs in photocatalytic directions and to develop more active photocatalytic systems.

Multi-Wire Sawing of Translucent Alumina Ceramics

Multi-wire sawing has emerged as the leading technology in wafer production for a variety of semiconductor materials. This study investigates the process stability and efficiency of conventional semiconductor multi-wire slurry saws in routinely machining translucent, high-density alumina ceramics. The brittle and fine-grained translucent alumina ceramics with extreme hardness and wear resistance represents a major challenge for the process. The alumina ceramic substrates are used for sensor applications, energy storage technology and applications in power electronics. An ideal adaptation of the sawing process parameters to the workpiece properties guarantees the efficiency of the slurry sawing process and the quality of the ceramic wafers. An indicator of the efficiency and cutting ability of the sawing process is the size of the bow of the wire web. The first time was shown that the wire bow can be used for the characterization of the sawing processes for hard and brittle technical ceramics. It was found that a longer workpiece length, a higher number of wafers and stronger abrasive wear lead to an increased size of the bow. The rocking frequency has no measurable influence on the size of the bow. Knowledge of these relations is an extremely valuable tool in the sawing process development for hard and brittle technical ceramics.

Open circuit voltage increase of GaSb/GaAs quantum ring solar cells under high hydrostatic pressure

Hydrostatic pressure can be used as a powerful diagnostic tool to enable the study of lattice dynamics, defects, impurities and recombination processes in a variety of semiconductor materials and devices. Here we report on intermediate band GaAs solar cells containing GaSb quantum rings which exhibit a 15% increase in open-circuit voltage under application of 8 kbar hydrostatic pressure at room temperature. The pressure coefficients of the respective optical transitions for the GaSb quantum rings, the wetting layer and the GaAs bulk, were each measured to be ~ 10.5 ± 0.5 meV/kbar. A comparison of the pressure induced and temperature induced bandgap changes highlights the significance of the thermal energy of carriers in intermediate band solar cells.

Conversion of an ultra-wide bandgap amorphous oxide insulator to a semiconductor

The variety of semiconductor materials has been extended in various directions, for example, to very wide bandgap materials such as oxide semiconductors as well as to amorphous semiconductors. Crystalline β-Ga2O3 is known as a transparent conducting oxide with an ultra-wide bandgap of ~4.9 eV, but amorphous (a-) Ga2Ox is just an electrical insulator because the combination of an ultra-wide bandgap and an amorphous structure has serious difficulties in attaining electronic conduction. This paper reports semiconducting a-Ga2Ox thin films deposited on glass at room temperature and their applications to thin-film transistors and Schottky diodes, accomplished by suppressing the formation of charge compensation defects. The film density is the most important parameter, and the film density is increased by enhancing the film growth rate by an order of magnitude. Additionally, as opposed to the cases of conventional oxide semiconductors, an appropriately high oxygen partial pressure must be chosen for a-Ga2Ox to reduce electron traps. These considerations produce semiconducting a-Ga2Ox thin films with an electron Hall mobility of ~8 cm2V−1 s−1, a carrier density Ne of ~2 × 1014 cm−3 and an ultra-wide bandgap of ~4.12 eV. An a-Ga2Ox thin-film transistor exhibited reasonable performance such as a saturation mobility of ~1.5 cm2 V−1 s−1 and an on/off ratio >107.

Advanced Raman Spectroscopy Using Nanofocusing of Light

Raman spectroscopy is uniquely sensitive to crucial material properties like stress and composition, but is inherently diffraction‐limited, impeding its application potential in nanostructured devices. Under correct polarization conditions, the Raman response from a periodic array of fins is dramatically enhanced inside the semiconductor material, re‐enabling fast and non‐destructive optical characterization of deep‐subwavelength semiconductor patterns. In this paper, it is shown that the effect is not limited to the material system where it was first observed, and results of nanofocused Raman spectroscopy in a variety of semiconductor materials are presented. The authors illustrate and discuss how the universality of the enhancement creates a unique potential for non‐invasive and rapid stress and composition measurements at the nanoscale.

Long-term production of H2 over Pt/CdS nanoplates under sunlight illumination

To seek robust active photocatalysts for sunlight-driven water splitting, a variety of semiconductor materials have been developed to achieve high photocatalytic efficiency. In this work, the CdS nanoplates with rough surface have been synthesized through a two-step ionic-exchange route. The as-synthesized sample was modified by Pt in an in situ photo-deposition cell to fabricate hybrid Pt/CdS nanophotocatalyst. The rate of average solar hydrogen evolution over the Pt/CdS nanoplates reached 3.75mmolh−1g−1, which is significantly higher than that of bare CdS and NiS/CdS counterparts. Furthermore, the Pt/CdS exhibited very high stability in continuous solar H2 evolution at a relatively stable state even over a 16-day reaction period, implying the as-fabricated hybrid nanophotocatalyst is approaching the practical requirements. The significantly enhanced photocatalytic efficiency was ascribed to the merits of rough plate-like nanostructures and the assistance of Pt co-catalyst, which can promote the light-absorption capability and photo-carrier separation as well as provide reactive sites. The present work opens an avenue to construct efficient and stable solar-driven catalysts for new energy creation.

Dislocation density-dependent quality factors in InGaN quantum dot containing microdisks

Microdisks incorporating InGaN quantum dots were fabricated using SiO2 microspheres as a hard mask in conjunction with a photoelectrochemical etch step from a structure containing a sacrificial InGaN/InGaN superlattice. Formation of microdisks from two near-identical structures with differing dislocation densities was carried out and investigated using microphotoluminescence. This confirmed the existence of quantum dots through the presence of resolution limited spectral lines and showed a clear correlation between the resulting modes quality factors and the dislocation densities within the disks. The disks with higher dislocation densities showed up to 80% lower quality factors than the low dislocation density disks.

Tritiation of Semiconductor Materials for Micropower Application

We report on a simple and versatile method for the integration of tritium in semiconductor materials. A variety of semiconductor materials are exposed to tritium (T2) gas at pressures of up to 120 bar and temperatures of up to 250 °C. Tritiated materials include hydrogenated amorphous silicon (a-Si:H), crystalline silicon (c-Si), silica and carbon nanotubes (CNT). Deep ultra-violet laser irradiation was used to lock tritium in silica films. Effusion measurements show the presence of stable tritium in silicon, silica and CNTs up to 400 °C. IR absorption spectra show a Si-T stretching mode at 1200 cm-1 indicating the formation of stable Si-T bonds in a-Si:H. SIMS measurements show that the penetration depth of tritium in a-Si:H and c-Si is 150 and 10 nm, respectively; the concentration of tritium locked in a-Si:H and c-Si is 20 and 4 at.%, respectively. In tritiated silica, 248-nm UV laser irradiation locks the permeated tritium at stable chemical bonding sites in the silica lattice. Thermal effusion measurement shows that 0.5 wt.% tritium can be stably immobilized in CNTs. The application of tritiated silicon as a cold electron source is demonstrated.

A comparison of avalanche breakdown probabilities in semiconductor materials

Using a hard dead space impact ionization model, the dependence of breakdown probabilities on overbias ratio in single photon avalanche diodes is investigated theoretically in a variety of semiconductor materials for the simple case of constant electric field, that is, in a p+-i-n+ diode structure. By using avalanche widths of 2 μm, the effects of dead space are minimized so that the breakdown probability results are determined primarily by the enabled ionization coefficients of the materials. The results illustrate how the slope of breakdown probability with overbias ratio is affected by the enabled ionization coefficients ratio and by the field dependences of ionization coefficients, which should be taken into account when choosing semiconductor materials for single photon avalanche diodes.

Intrinsic limitations to the doping of wide-gap semiconductors

Doping limits in semiconductors are discussed in terms of the amphoteric defect model (ADM). It is shown that the maximum free electron or hole concentration that can be achieved by doping is an intrinsic property of a given semiconductor and is fully determined by the location of the semiconductor band edges with respect to a common energy reference, the Fermi level stabilization energy. The ADM provides a simple phenomenological rule that explains experimentally observed trends in free carrier saturation in a variety of semiconductor materials and their alloys. The predictions of a large enhancement of the maximum electron concentration in III–N–V alloys have been recently confirmed by experiment.

Materials for Mid-Infrared Semiconductor Lasers

AbstractA variety of semiconductor materials have been used to fabricate diode lasers for the midinfrared. Lasers using the lead salts (e.g. PbSnTe) have been commercially available for some time. Mid-infrared emitting III-V semiconductors (e.g. InGaAsSb) have superior thermal conductivity, and diode lasers fabricated from these materials offer higher powers. Of particular interest are the III-V semiconductor lasers based on type-II superlattices (e.g. InAs/GaInSb). Among the many unique properties attributed to type-Il superlattices are small hole mass, reduced Auger recombination, and less inter-valence band absorption - all important for better lasers. Recent results with Quantum Cascade-type lasers are also very encouraging. This paper summarizes the important semiconductor materials for mid-infrared lasers with emphasis on the type-II superlattices.

Role of molecular beam epitaxy in the optoelectronic field

Abstract Having celebrated its twenty-second anniversary, molecular beam epitaxy (MBE) has reached a very mature state as a crystallographic growth technique for a variety of semiconductor materials. It is widely used at universities, for industrial research in development laboratories and in production. Companies currently sell devices made from MBE-grown materials such as high-electron-mobility transistors (HEMTs), GaAs/AlGaAs lasers, photodetectors etc. The success of MBE technology can be explained by some of its inherent strengths. It uses extremely high-purity source material inside a vacuum chamber, making its operation predictable and safe. The growth process is relatively simple and can be monitored by in situ analysis tools. MBE played a key role in the exploration of new material systems such as GaAs on silicon and strained layers. Today's technology, together with the immense knowledge and understanding of growth aspects, makes it possible to achieve ultrathin layers, abrupt heterointerfaces and three-dimensional band gap engineering by growth on non-planar or tilted substrates. Areas in the optoelectronic field in which MBE has made substantial contributions are therefore III–V layers on silicon, including photodetectors and lasers, ultralow threshold and very high-power Ga(In)As/AlGaAs lasers, surface-emitting lasers which require very precisely controlled and stable fluxes, long-wavelength photodetectors, non-planar substrate devices etc. Areas that are more difficult to explore with MBE but are nevertheless very challenging include selective area growth and material systems from groups other than III and V which contain gallium, aluminum, indium and arsenic. Furthermore, newer fields such as low-dimensional structures with all kinds of in situ formations as well as further improvement of the MBE technology, including better diagnostic tools and group V flux controls etc., will engage the MBE community for several years to come.

A simple rotating jet-thinning apparatus for producing taper sections and electron microscope specimens from silicon and compound semiconductors

Descriptions are given of a jet-thinning apparatus which rotates the specimen in the jet stream, and a method of producing continuously chlorinated methanol via a double concentric emulsifier jet. The system has been successfully used to produce uniform electron microscope specimens from a variety of semiconductor materials, and by double-sided thinning, buried heterojunction dislocation networks have been examined.Examples are also given of the use of the apparatus for preparing shallow angle taper sections for examination by chemical staining methods. With the use of the internal interference fringes, the depth of of staining at p-n junctions etc has been measured to better than 500 Å. The advantages of chemically prepared taper sections over conventional mechanically lapped specimens are discussed.

Scribe‐Plating and ‐Etching

A technique is described which permits the fabrication of miniature and microminiature ohmic and doped contacts in complex configurations on a variety of semiconductor materials. This technique involves the preferential nucleation of chemiplated and electroplated metals on microscopically fine lines scribed on semiconductor surfaces and the preferential etching of similarly scribed lines. Lines of the order of 10−4 cm have been plated with a variety of metals including doping elements. Scribe plating has yielded p‐n junctions and offers promise of the fabrication of p‐n junction devices considerably smaller than those currently available. This technique is also potentially useful in the fabrication of conventionally sized devices, some of which are described. Suggestions are advanced for the use of this technique in both microminiature and other device fabrication.